Electrical plug with selectable grounding terminals

ABSTRACT

An electric plug for connecting a three-wire electrical system to a three-prong or two-prong electric receptacle comprising, generally, a plug having the conventional two current-carrying prongs and a top portion, manually adjustable, to present a third, ground prong, for reception in a conventional three-prong receptacle or a pigtail for connection to the conventional metal wall box of a two-prong receptacle. The top portion is manually adjustable in a manner whereby either the ground prong or the pigtail is disposed in electrical connection with the third, ground wire, in the wire cable to the plug while the grounding terminal not in use is disconnected therefrom.

llnited States Patent Garrett ELECTRICAL PLUG WITH SELECTABLE GROUNDING TERMINALS Inventor: Lewis B. Garrett, 1020 W. 47th St.,

Hialeah, Fla. 33012 [22] Filed: Nov. 12, 1973 [21] Appl. No.: 415,144

[52] U.S. Cl 339/14 RP, 339/31, 200/51 R [51] Int. Cl H0lr 3/06 [58] Field of Search 339/14, 31, 32, 33; 200/51 [56] References Cited UNITED STATES PATENTS 2,846,530 8/1956 Wintriss 200/51 R 2,986,718 5/1961 Bender 339/14 RP 3,299,390 1/1967 Eckelkamp 339/12 R [451 July 23,1974

Primary Examiner-Bobby R. Gay Assistant Examiner-Robert A. l-lafer [57] ABSTRACT An electric plug for connecting a three-wire electrical system to a three-prong or two-prong electric receptacle comprising, generally, a plug having the conventional two current-carrying prongs and a top portion,

manually adjustable, to present a third, ground prong, for reception in a conventional three-prong receptacle or a pigtail for connection to the conventional metal wall box of a two-prong receptacle. The top portion is manually adjustable in a manner whereby either the ground prong or the pigtail is disposed in electrical 1 connection with the third, ground wire, in the wire cable to the plug while the grounding terminal not in use is disconnected therefrom.

13 Claims, 5 Drawing Figures new ELECTRICAL PLUG WITH SELECTABLE GROUNDING TERMINALS STATE OF THE PRIOR ART Many electrical appliances and virtually all power tools, particularly those designed to be held in the operators hands are provided with three wire systems, two current-carrying wires and a ground wire. As a result such appliances, tool, etc. are equipped with threeprong plugs, the third prong being intended for reception in the ground terminal of a conventional threeprong receptacle.

It is a well known fact that the ground connection is a safety factor, particularly for any type of electric tool, appliance, etc. that has or can have any contact with a person or persons while in use. Most wall receptacles are of the conventional type which are adapted to receive only the two current-carrying prongs of a plug with the exception of those that are installed adjacent to the location of a major appliance which, it is known, will require athree-prong receptacle. As a result, when it becomes necessary to plug in an electrically operated device such as a power tool, for example, with a three wire system, it is necessary to employ an adaptor plug which includes a female side for receiving the three prongs 'of the device and a male side providing two prongs for reception in a conventional two-prong receptacle. Conventional adaptors of this type include a ground wire, commonly called a pigtail including a fork on the extended end for connection to the plug mounting box through the screw which connects the cover plate thereto.

US. Pat. No. 3,299,390 to L. Eckelkamp discloses an electric connector with a grounding terminal. This connector includes a bottom portion with the conventional two prongs, internally connected to the currentcarrying wires from the three wire cable and an upper portion, pivotally connected to the lower portion. Extending outwardly from one end of the upper portion is a generally conventional type of ground prong and from the other end thereof, is a projecting magnetic ground plate. The ground wire connects with both the ground plug and magnetic plateat all times through a metal pivotjconnectingthe two portions together.

OBJECTS AND ADVANTAGES OF THE PRESENT INVENTION portion providing the two conventional currentpresented for connection with either a two or threeprong receptacle.

carrying prongs and a top'portion having a ground prong projecting outwardly from one end thereof and a pigtail ground connected at the opposed end.

Yet another object of this invention is to make the top portion of the plug reversible relative to the bottom portions, the proper ground connection thereby being A further object of the present invention is to provide a single electrical connection from the cable ground wire to a contact intermediate the bottom and top plug portions for contact with whichever one of the two ground terminals is disposed on the same sideof the plug as are the two current-carrying prongs. The aforementioned prior art Patent provides opposed ground terminals, both of which are always in electrical connection to the cable ground wire, resulting in a potential danger to anyone coming into contact with the unused ground terminal or with an appliance or tool, for example, which may have been inadvertently moved into contact therewith. This type of plug presents a second potential danger because the magnetic ground plate, when in use simply bears against the outer surface of the screw which holds the cover plate over the wall box. Particularly with power hand tools, the threewire cable to the plug is constantly in motion when the tool is in use. This often results in movement being transmitted to the plug in a manner whereby said plug may be moved or partially dislodged to a point where power contact between the two current-carrying prongs and the receptacle is not interrupted. However,

the plug may be moved to a position whereby, without BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the electrical plug of the present invention;

FIG. 2 is a longitudinal sectional view of the plug illustrated in FIG. 1, illustrating a ground plug disposed for reception in a three-prong receptacle;

FIG. 3 is a view similar to FIG. 2 but illustrating a pigtail ground in a position for grounding purposes;

FIG. 4 is a view similar to FIG. 2 illustrating a first modified form of the invention; and

FIG. 5 is a view similar to FIGS. 2 and'4 illustrating a second modified form of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS ally of a lower portion 12 formed of a suitable insulating material and an upper portion 14, similarly formed. Projecting from a first end 16 of the lower portion are a pair of current-carrying prongs l8 and 20. A conventional type of three wire electrical cable 22 enters the second, opposed end 23 of the lower section,containing two current-carrying'wires 24 and 26, and a ground wire 28.

The upper portion provides a first end 30 having a first ground terminal in the form of a plug 32 projecting outwardly therefrom for reception, along with the prongs l8 and 20, in a conventional three-prong receptacle. A second ground terminal in the form of a pigtail 34 is fixed by a screw 36 to the second, opposed end 38 of the upper portion for grounding purposes when it is necessary. to plug into a conventional two-prong receptacle.

With reference to FIG. 2, the cable 22 is preferably,

and the two current-carrying wires 24 and 26 are fixed to the inner end portions, such as 42, of the prongs 18 and 20 (only one prong being shown in FIGS. 2 and 3).

The third, ground wire 28 is similarly fixed as at 44 to a vertically disposed first receptacle 46, molded into the upper side of the lower plug portion 12 and opening outwardly thereof. A second, similar receptacle 48, is molded into the lower plug in a like manner, however, it has no connection to the ground wire 28. The receptacle 46 and 48 are equally spaced relative to the opposed sides of the center axis X through the plug 10.

The ground prong 32 projecting outwardly from the first end 30 of the upper plug portion 14 includes an inner end portion 50 which, along with a downwardly projecting first prong portion 52, are molded into said upper plug portion 14. A first extension 54 of the prong portion 52 engages in the receptacle 46 when the ground plug 32 is disposed for reception in a threeprong receptacle.

With further reference to FIG. 2, the pigtail 34 is attached by the screw 36 to a plate 56 lying horizontally atop the opposed upper end portion 38; said plate 56 provides a second downwardly extending prong portion 58, molded into said upper plug portion 14, and a second extension 60 therefrom which engages in the second receptacle 48 when the ground plug 32 is in use.

The pigtail 34 includes a first fork connector 62, engaged between the screw 36 and plate 56 and a second, outer end fork connector 64 which is adapted for engagement by the connector screw 66 (FIG. 3), holding the cover plate 68 relative to a wall box (not shown), containing a two-prong receptacle R.

When the electrical plug is used for insertion into a conventional three-prong receptacle, the upper plug portion is disposed in the position above described relative to FIG. 2; when used for insertion into a conventional two-prong receptacle, the upper plug portion 14 is manually removed from the first and second receptacles 46 and 48, rotated 180 degrees and reconnected with the first prong extension 54 engaged in the second receptacle 48 and the second prong extension 60 en-- gage in the first receptacle 46.

Therefore, it can be seen that the pigtail 34 is in electrical connection with the ground wire 28 and is effectively grounded by its connection at the outer fork end 64 to the receptacle box through the screw 66. The plug 32 is then completely disconnected from the ground wire 28 and poses no danger from direct or indirect contact therewith.

FIG. 4 illustrates a first modification of the present invention and will be described in detail only insofar as the modified structural details are concerned, the like or corresponding elements being designated by primes.

The first prong portion 52' is fixed to a first detent socket 70 disposed in the bottom surface of the upper plug portion 14' and a second detent socket 72 fixed to the second prong portion 58 is similarly disposed on the opposed side of the axis X. A steel detent ball 74, compression spring 76 and electrical connector 78, connected to the ground wire 28, are disposed in a recess 80 through the top surface of the lower plug portion 12 inwardly of the first or ground prong side thereof.

A pivot pin 82 having headed, opposed ends 84 and 86, molded respectively into the lower and upper plug sections 12' and 14', along the axis X:", permits the upper plug section 14 to be rotated 180 relative to the lower plug section 12' to selectively dispose the prong 32 or pigtail 34' into an operable position relative to a three or two prong receptacle in the same manner as described relative to the form of the invention disclosed and described in FIGS. 1, 2 and 3, the ground connection being completed through either the prong 32 or pigtail 34', the prong portion 52' or 58 and the ball, spring and connector 74, 76 and 78 to the ground wire 28. The second detent 72 may be provided with a detent ball, and compression spring 88 and 90 in a recess 92 to provide a balanced operation of the plug 10.

With reference to FIG. 5, a second modification of the present invention is disclosed, all like or corresponding parts being designated by double primes. The lower plug portion provides an internal cavity 94, the lower headed end 84" of the pivot pin 82" being freely disposed therein. A compression spring 96 is positioned about the pin 82 in the internal cavity 94 between the lower headed end 84" and a ground conductor plate 98, embedded in the lower plug portion 12". Ground wire 28" connects with the conductor plate 98, which, in turn, connects with a first receptacle 100 which is adapted to receive a first prong 102, fixed to the lower end of the first prong portion 52" from the ground prong 32". A second receptacle 104 is positioned in an opposed relation to receptacle 100 and seats a second prong 106, fixed relative to the lower end of the second prong portion 58".

The respective prongs 102 and 106, and receptacles 100 and 104 are preferably formed in a male and female conical configuration to insure a good electrical connection between either prong 102 or 106 and the receptacle 100.

As best seen in FIG. 1, the opposed sides of the plug 10" are longitudinally concave to provide finger grip means whereby the upper plug portion 14" may be raised against the forces of the compression spring 96 and rotated degrees in either direction to selectively seat either the prong 102 or 106 in the receptacle 100 to complete a ground circuit to either the prong 32" or pigtail 34" through the plate 98 to the ground wire 28".

In like manner the plugs 10 and 10' of the first two forms of the invention as illustrated and described, are provided with longitudinally concave sides to facilitate the necessary movements of the top portions thereof to selectively position the respective ground connections relative to a receptacle.

What is claimed is:

1. An electric plug with selectable grounding terminals for connection between a three wire system having two current-carrying wires and a ground wire, and either a three-prong or two-prong receptacle, said electric plug comprising;

A. a main lower portion having,

I. a first end,

2. a second end,

3. a pair of current-carrying prongs fixed within said lower portion in respective electrical connection with the two current-carrying wires and projecting outwardly through said first end for reception in the two conventional currentcarrying female receptors in either a two three-prong receptacle, and

4. electric conductor means from the ground wire within said lower portion to a single electric contact means thereatop;

B. an upper portion having,

1. a first end,

2. a second end,

3. a ground prong projecting outwardly of said first end,

4. a pigtail ground fixed adjacent to said second end, and

5. first and second conductor means from the respective ground plug and pigtail to a first and second electric contact means;

C. means to provide for rotational movement of said upper portion to selectively dispose either of said first or second electriccontact means in electrical contact with said single contact means, whereby said ground prong when so electrically connected is positioned relative to said current-carrying prongs for reception in a conventional three-prong receptacle, or said pigtail ground is positioned relative to said current-carrying prongs to provide for a grounded connection relative to a conventional two-prong receptacle installation.

2. The electric plug as defined in claim 1 wherein said electric conductor means from the ground wire and sin- 4 gle electric contact means comprises an open top conductor receptacle extending downwardly through the top wall of said main lower portion adjacent said first end thereof.

3. The electric plug as defined in claim 2 wherein said first and second conductor means from the respective ground plug and pigtail ground comprises a prong from each of same extending a Predetermined distance below the bottom surface of said upper portion.

4. The electric plug as defined in claim 3 including a non-conductor open top receptacle extending downwardly through the top wall of said main lower portion adjacent said second end thereof; said conductor and non-conductor receptacles being positioned to slidably receive said prong extensions to selectably complete an electric circuit, in either combination, to said ground prong or pigtail.

5. The electric plug as defined in claim 1 wherein said first and second conductor means from the respective ground prong and pigtail ground comprises a prong from each of same connecting to a detent socket in the bottom face of said upper portion.

6. The electric plug as defined in claim 5 wherein said single electric contact means and electric conductor means comprises a first detent ball and compression spring in a recess, opening downwardly through the top wall of said main lower portion, said spring extending in contact between said detent ball and ground wire.

7. The electric plug as defined in claim 6 including a pivot means connecting between said upper and main lower portions whereby said upper portion is rotatable relative to said main lower portion to selectably engage said first detent ball in either of said detent sockets to complete a ground circuit to either the ground prong or pigtail ground.

8. The electric plug as defined in claim 7 including a second non-conductor detent ball and compression spring in a second recess opening downwardly through the top wall of said main lower portion in a position whereby said non-conductor ball seats in the detent socket not in connection with the ground wire.

9. The electric plug as defined in claim 1 wherein said first and second conductor means from the respective ground prong and pigtail ground comprises a connector prong from each of same, connecting to a prong portion extending downwardly below the lower face of said upper portion.

10. The electric plug as defined in claim 9 including a ground conductor plate embedded in said lower portion connecting between the ground wire and a first, conductor receptacle positioned to receive either of the downwardly extending prong portions.

11. The electric plug as defined in claim 10 including a second, non-conductor receptacle in said main lower portion, positioned to receive either of the downwardly extending prong portions.

12. The electric plug as defined in claim 11 including an internal cavity, longitudinally, centrally positioned in said main lower portion, a centrally disposed pivot means connecting between said upper and main lower portions and a compression spring disposed in said cavity between the top thereof and an enlarged, lower head portion of said pivot means extending into said cavity, whereby said upper plug portion may be lifted away from said main lower portion, against the forces of said compression spring, to permit said upper portion to be rotated relative to said lower portion for selective seating engagement between the respective prong extensions and said conductor and nonconductor receptacles.

conductor and non-conductor receptacles are in the form of respective interengaging male and female conical members. 

1. An electric plug with selectable grounding terminals for connection between a three wire system having two currentcarrying wires and a ground wire, and either a three-prong or two-prong receptacle, said electric plug comprising; A. a main lower portion having,
 1. a first end,
 2. a second end,
 3. a pair of current-carrying prongs fixed within said lower portion in respective electrical connection with the two current-carrying wires and projecting outwardly through said first end for reception in the two conventional currentcarrying female receptors in either a two or three-prong receptacle, and
 4. electric conductor means from the ground wire within said lower portion to a single electric contact means thereatop; B. an upper portion having,
 1. a first end,
 2. a second end,
 3. a ground prong projecting outwardly of said first end,
 4. a pigtail ground fixed adjacent to said second end, and
 5. first and second conductor means from the respective ground plug and pigtail to a first and second electric contact means; C. means to provide for rotational movement of said upper portion to selectively dispose either of said first or second electric contact means in electrical contact with said single contact means, whereby said ground prong when so electrically connected is positioned relative to said current-carrying prongs for reception in a conventional three-prong receptacle, or said pigtail ground is positioned relative to said currentcarrying prongs to provide for a grounded connection relative to a conventional two-prong receptacle installation.
 2. a second end,
 2. a second end,
 2. The electric plug as defined in claim 1 wherein said electric conductor means from the ground wire and single electric contact means comprises an open top conductor receptacle extending downwardly through the top wall of said main lower portion adjacent said first end thereof.
 3. a ground prong projecting outwardly of said first end,
 3. a pair of current-carrying prongs fixed within said lower portion in respective electrical connection with the two current-carrying wires and projecting outwardly through said first end for reception in the two conventional current-carrying female receptors in either a two or three-prong receptacle, and
 3. The electric plug as defined in claim 2 wherein said first and second conductor means from the respective ground plug and pigtail ground comprises a prong from each of same extending a Predetermined distance below the bottom surface of said upper portion.
 4. The electric plug as defined in claim 3 including a non-conductor open top receptacle extending downwardly through the top wall of said main lower pOrtion adjacent said second end thereof; said conductor and non-conductor receptacles being positioned to slidably receive said prong extensions to selectably complete an electric circuit, in either combination, to said ground prong or pigtail.
 4. electric conductor means from the ground wire within said lower portion to a single electric contact means thereatop; B. an upper portion having,
 4. a pigtail ground fixed adjacent to said second end, and
 5. first and second conductor means from the respective ground plug and pigtail to a first and second electric contact means; C. means to provide for rotational movement of said upper portion to selectively dispose either of said first or second electric contact means in electrical contact with said single contact means, whereby said ground prong when so electrically connected is positioned relative to said current-carrying prongs for reception in a conventional three-prong receptacle, or said pigtail ground is positioned relative to said current-carrying prongs to provide for a grounded connection relative to a conventional two-prong receptacle installation.
 5. The electric plug as defined in claim 1 wherein said first and second conductor means from the respective ground prong and pigtail ground comprises a prong from each of same connecting to a detent socket in the bottom face of said upper portion.
 6. The electric plug as defined in claim 5 wherein said single electric contact means and electric conductor means comprises a first detent ball and compression spring in a recess, opening downwardly through the top wall of said main lower portion, said spring extending in contact between said detent ball and ground wire.
 7. The electric plug as defined in claim 6 including a pivot means connecting between said upper and main lower portions whereby said upper portion is rotatable relative to said main lower portion to selectably engage said first detent ball in either of said detent sockets to complete a ground circuit to either the ground prong or pigtail ground.
 8. The electric plug as defined in claim 7 including a second non-conductor detent ball and compression spring in a second recess opening downwardly through the top wall of said main lower portion in a position whereby said non-conductor ball seats in the detent socket not in connection with the ground wire.
 9. The electric plug as defined in claim 1 wherein said first and second conductor means from the respective ground prong and pigtail ground comprises a connector prong from each of same, connecting to a prong portion extending downwardly below the lower face of said upper portion.
 10. The electric plug as defined in claim 9 including a ground conductor plate embedded in said lower portion connecting between the ground wire and a first, conductor receptacle positioned to receive either of the downwardly extending prong portions.
 11. The electric plug as defined in claim 10 including a second, non-conductor receptacle in said main lower portion, positioned to receive either of the downwardly extending prong portions.
 12. The electric plug as defined in claim 11 including an internal cavity, longitudinally, centrally positioned in said main lower portion, a centrally disposed pivot means connecting between said upper and main lower portions and a compression spring disposed in said cavity between the top thereof and an enlarged, lower head portion of said pivot means extending into said cavity, whereby said upper plug portion may be lifted away from said main lower portion, against the forces of said compression spring, to permit said upper portion to be rotated relative to said lower portion for selective seating engagement between the respective prong extensions and said conductor and non-conductor receptacles.
 13. The electric plug as defined in claim 12 wherein said pair of downwardly extending prong portions and conductor and non-conductor receptacles are in the form of respective interengaging male and female conical members. 